Beam tube and circuitry therefor



1956 M. 1. DISMAN ETAL 3, 7,

BEAM TUBE AND CIRCUI'I'RY THEREFOR Filed July 15, 1961 2 Sheets-Sheet 1 a PE IN V EN TORS MURRAY I. DISMAN SAMUEL J M/LLWARD ALBERT M/ZUHARA ATTORNEY Jan. 4, 1966 M, DlsMAN ETAL 3,227,913

BEAM TUBE AND CIRCUITRY THEREFOR Filed July 13, 1961 2, Sheets-Sheet 2 INVENTORS MURRAY I. DISMAN SAMUEL J. MILLWARD BY ALBERT MIZUHARA Mac My s ATTORNEY United States Patent 3,227,913 BEAM TUBE AND CIRCUITRY THEREFOR Murray I. Disman, Sunnyvale, Samuel J. Millward, Menlo Park, and Albert Mizuhara, San Mateo, Calif., assignors to Eitel-McCullough, Inc., San Carlos, Califi, a corporation of California Filed July 13, 1961, Ser. No. 123,876 5 Claims. (Cl. 315-35) The invention relates to electron beam tubes and associated apparatus, and particularly to traveling wave tubes and permanent periodic magnetic focusing circuits therefor.

A search through the prior art that has developed relating to traveling wave tubes reveals that whereas many hundreds of patents have been issued relating to traveling wave tube operating principles, very few of these patents teach the basic fundamentals required for constructing a commercially feasible traveling wave tube structure.

Conventional traveling wave tubes comprise an elongated envelope, generally glass, within one end of which is situated an electron gun designed to project a narrow beam of electrons the length of the envelope, the beam being collected in an appropriate collector situated in the end of the envelope remote from the electron gun. Interposed between the electron gun and collector is an interaction or slow wave structure, commonly a small diameter helix, through the exact center of which the electron beam is projected. A problem usually exists with regard to the means for maintaining the helix coaxially centered within the envelope. To secure interaction between a radio frequency signal desired to be amplified and the electron beam projected through the envelope, one end of the helix is conventionally connected to a radio frequency input terminal, while the other end of the helix is connected to a radio frequency output terminal. The length and pitch of the helix is correlated to the beam velocity and frequency of the radio frequency input signal so that the forward velocity of the signal coincides with the beam velocity.

It is accordingly one of the important objects of this invention to provide a traveling wave tube structure which gives consideration to the varied fundamental principles regarding traveling wave tubes, and accomplishes this in a practical structure capable of being manufactured economically and efiiciently to provide a traveling wave tube capable of incorporation in almost any environment.

For maximum efliciency and high gain, it is desirable that the electron beam have a high perveance, but this results in high mutual repulsion between the electrons. Such mutual repulsion tends to cause the electrons to disperse, and unless restricted by some means, the electrons of the beam impinge on the surrounding structure, particula-rly the helix, causing the tube to overheat. To prevent such spreading of the electrons, it is customary in most conventional traveling wave tubes to confine the beam by extrinsic means or circuits generating a magnetic field. Conventional traveling Wave tubes usually utilize electromagnetic beam guiding systems or permanent magnet beam guiding systems. More recently, magnetic systems made up of a multiplicity of axially spaced permanent magnets to provide a periodic beam guiding system have been utilized. Most of these beam guiding magnetic systems are fraught with problems, one of which constitutes the means by which the radio frequency input and output terminals are extended through the magnetic field into the envelope to connect with the opposite ends of the helix without disturbing the uniformity or distribution of the magnetic field. It is therefore another object of the invention to provide radio frequency input and output coupling means completely isolated from the magnetic beam guiding system.

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Still another problem is the attachment of such beam guiding magnets on the smooth exterior of a traveling wave tube body. It is therefore another object of this invention to provide a permanent periodic magnetic circuit completely surrounding a smooth tubular portion of the traveling wave tube cooperating with means for securing such stack immobile on the tube.

In all traveling wave tubes, extreme temperature differentials, whether caused by operation of the tube or by the ambient temperature of its environment, create many problems. One of such problems involves the means of dissipating heat from the collector portion of the tube. It is therefore a still further object of this invention to provide a cooler for a traveling wave tube which is cooperatively related to surrounding structure in a manner permitting facility of attachment and detachment and efficiency in the dissipation of heat.

Another of such problems caused by temperature differentials in traveling wave tubes relates to the expansion and contraction of various elements of the tube, and the maintenance of desired electrical operating characteristics through such heat cycling. Experience in this field has shown that while a traveling wave tube may appear on the drawing board to be exceptionally well designed, as soon as the tube is built and power is applied, the increase in temperature of various members of the combination often results in misalignment occurring such as to cause the electron beam to impinge on related structure rather than to follow its proper path. It is therefore another important object of this invention to provide a traveling Wave tube structure in which the cooperative relationship of parts under actual operating conditions precludes such misalignment.

Conventional traveling wave tubes are susceptible to impact shock and vibration, and misalignment of tube elements resulting from such shocks and vibration often alters the proper functional relationship of tube elements. It is therefore a still further object of the present invention to provide a traveling wave tube structure capable of encapsulation to minimize the eflect of such impact shocks and vibration on the internal structure.

Traveling Wave tubes of whatever design constitute extreme-1y complicated mechanisms, costly to manufacture from the standpoint of materials and labor. It is therefore desirable that such tubes be designed for construction in a manner to permit salvage of reusable parts from tubes which must be discarded. It is therefore another object of the invention to provide a traveling wave tube structure in which the envelope may be opened to effect replacement or repair of damaged parts.

In terms of the effectiveness of the traveling wave tube to do the job which it is designed to do, one of the most critical areas is the electron gun structure. Faulty design of the electron gun can result in tubes being consistently defective. It is therefore .another object of the present invention to provide a novel electron gun structure especially adapted for use with a traveling wave tube.

Because of their complexities, traveling wave tubes often sell for many thousands of dollars, notwithstanding the fact that the tube may be only about 15 inches long and perhaps an inch in overall diameter. Such cost results from the necessity, heretofore, of substantially custom building each tube from beginning to end. It is therefore another object of this invention to provide a traveling wave tube structure capable of being frabricated and assembled by mass production techniques, resulting in lower costs and reproducibility of tubes having the same characteristics.

Most conventional traveling Wave tubes, as previously stated, include a brittle glass envelope susceptible of being easily broken. Even a small crack in a glass envelope will render a traveling wave tube useless. It is therefore another object of the present invention to provide an electron tube structure constituted of metal and ceramic parts integrally brazed to provide a strong and rugged structure.

The invention possesses other objects and features of advantage, some of which, with the foregoing, will be set forth in the following description of the invention. It is to be understood that the invention is not limited to the embodiment described in the specification and illustrated in the accompanying drawings, but may be embodied in various ways within the scope of the appended claims.

Broadly considered, it is an advantage in most manufacturing processes to design individual elements for economy and facility of manufacture, and to design sub-assemblies to permit facility of assembly of such elements. Proper design of the sub-assemblies then permits their association into a composite whole in a manner which ensures proper tolerances between cooperating elements of adjacent sub-assemblies. Such manufacturing processes and procedures contribute to the uniformity or reproducibility of identical elements and sub-assemblies, and therefore to the reproducibility of similar electrical characteristics in different tubes. In the structure constituting the subject matter of the present invention, therefore, the tube is comprised, broadly speaking, of three coaxially arranged tubular envelope sections constituting a gun section, an interaction section, and a collector section. These tubular sections are coaxially arranged about a central longitudinal axis and have associated ends integrally brazed one to the other to provide rigidity. This arrangement makes it possible to treat each of the sections as a sub-assembly, which may be separately fabricated and then joined to the others. Arranged within the tubular gun section is a tubular assembly constituting the electron gun assembly. This assembly is preferably fabricated as a unit and slipped into position through the open end of the electron gun tubu lar section. Appropriately positioned abutments on the tubular envelope section and gun assembly cooperate to appropriately position the electron gun within the outer envelope section. An auxiliary anode independently mounted within the electron gun envelope section cooperates with the other electron gun elements to project a beam of electrons through the adjacent tubular interaction within which is appropriately supported a slow wave structure. The end of the envelope remote from the electron gun section is constituted by the third tubular envelope section, within which is mounted a collector. This envelope section is also designed to be fabricated as a separate assembly which may be readily attached to the end of the tubular interaction section. Window means are associated with the union of these two envelope sections to facilitate connection of the terminal end of the slow wave structure with the inner conductor of an output terminal coaxially arranged with respect to the collector envelope section. The other end of the slow wave structure is connected to the inner conductor of an input terminal in a manner to provide a proper match between the slow wave structure and the transmission line connected to the input terminal.

After the separate sub-assemblies of the traveling wave tube have been integrally united into a composite and rigid whole, the collector and interaction sections of the envelope are projected through a stack of annular permanent magnet wafers. Pole pieces are interposed between each of the wafers and engage the outer surface of the tube envelope in a snug slide fit. Gaps are provided between the inner peripheries of the adjacent pole pieces, while their outer peripheries are suitably connected by a multiplicity of compensating strips. This arrangement results in a multiplicity of magnetic fields axially spaced along the envelope sections, with a portion of each field extending into the envelope an amount to confine a portion of the beam. Collectively, the annular permanent magnets provide a tube of magnetic lines of force through which the beam is projected. A cooler assembly detachably mounted on the end of the tube adjacent the collector serves to clamp the stack of annular magnets on the tube envelope. In order to further retain the stack of magnets in a fixed position with regard to the envelope and each other, a tubular shell, preferably stainless steel, is provided concentrically surrounding the magnet stack to provide an annular space between the shell and the concentrically arranged compensating strips. Such space is filled with a self-polymerizing liquid dielectric material such as epoxy resin to encapsulate the magnet stack. When solidified, the encapsulating material constitutes a mass retaining the stack completely rigid While providing a cushion between exteriorly applied impact shocks and the shock-sensitive internal parts of the tube. To complete the encapsulation of the traveling wave tube, an other cylindrical sleeve is slipped over the electron gun section of the envelope into abutting relation with the first sleeve in a manner to provide an annular space which is suitably filled wtih dielectric material as before. Traveling wave tubes so constructed have been successfully subjected to temperature cycling in the range of 55 C. to 70 C., to vibration tests imposing vibrations of 5 to 500 cycles per second, and to accelerations of 10 GS at simulated altitudes of 70,000 feet.

Referring to the drawings:

FIGURE 1 is a vertical half-sectional view, a portion of the structure being broken away to reduce its length.

FIGURE 2 is an elevation of the traveling wave tube illustrated in FIGURE 1, shown apart from the magnetic structure. A portion of the tube is broken away to reduce its length.

FIGURE 3 is a vertical cross-section taken in the plane indicated by the line 33 in FIGURE 1.

FIGURE 4 is a vertical half-section of a modified gun construction.

FIGURES l and 2 are shown approximately twice actual size, while FIGURES 3 and 4 are shown approximately four times actual size.

In terms of greater detail, the beam tube forming the subject matter of this invention comprises a hollow thick walled metallic gun cup 2, having a uniform outside diameter and provided on its interior with shoulders 3 and 4 by counterboring the cylindrical wall of the cup to form concentric surface areas 6 and 7. The gun cup is open at one end, and at its other end is provided with a thick bottom 8 centrally apertured as shown. The gun cup forms a portion of the electron gun section of the beam tube, and includes within its confines an electron gun assembly designated generally by numeral 9, which includes accelerating anode 12. The accelerating anode includes short cylindrical section 13 having radially extending in tegral flange 14 extending therefrom. The outer peripheral edge of flange 14 is rabbeted as shown.

To coaxially support the accelerating anode within electron gun cup 2, a hollow shell 16 is provided, having a cylindrical portion 17 and a truncated conical portion 18, the apex end of which is integrally united as by spot welding to the peripheral rabbeted edge of flange 14 on the accelerating anode. As shown in the drawing, cylindrical portion 17 of the accelerating anode shell is integrally brazed on surface 6 within the electron gun cup 2. This insures that the accelerating anode will be coaxially arranged within the hollow gun cup. In order that isolated chambers shall not be formed within the electron gun cup, suitable apertures 19 are formed in the anode shell, preferably formed in the conical section and of sufficient size to reduce the weight of the structure while maintaining its mechanical rigidity. As shown in the drawings, the accelerating anode is axially spaced a short distance from bottom 8 of the electron gun cup.

The electron gun assembly 9 extends coaxially into the open end of electron gun cup 2. This assembly includes a hollow metallic shell 21, provided with a cylindrical portion 22 at one end and joined to intermediate cylindrical section 23 by integral conical section 24. A shoulder 26 separates cylindrical section 23 of the shell from a third cylindrical portion 27. Surrounding cylindrical section 23 of the shell is an annular dielectric spacer member 23. The shell fits snugly within the inner periphery of the dielectric spacer member, the outer periphery of which is scalloped and rests snugly within the interior of the cup on shoulder 4. Shell 21 is therefore rigidly retained coaxially within the electron gun cup.

In fabricating the electron gun cup and shell 21, the distance from the shoulder 4 to the bottom of the cup, and the diameter of the surface portion 7 within the cup, are closely controlled, as is the height of shell 21 between shoulder 26 and the end of cylindrical section 22. This makes it possible to exactly locate the electron gun assembly within the electron gun cup. The focus electrode 29, supported within the end of cylindrical section 22, and having a cylindrical section 31 and a conical section 32, is therefore accurately oriented with respect to the accelerating anode 12. In assembling the focus electrode within the cylinder 22, the outer peripheral edges are maintained flush and this determines proper location for the focus electrode. This electrode is of course apertured as at 33, which aperture is in axial alignment with the aperture through the accelerating anode.

Coaxially supported within shell 21 is a cathode support shell 34. Shell 34 is provided at one end with a radially outwardly extending flange 36, and adjacent its other end is provided with a radially inwardly extending flange 37 terminating in a cylindrical axially extending flange 38. To support shell 34 coaxially within shell 21, a dielectric spacer 39 is interposed between shell 34 and cylindrical section 27 of shell 21. Dielectric spacer 39 abuts flange 36 and shoulder 26 on shell 21. This relationship of parts accurately locates the cathode support shell with respect to the focus electrode support shell 21. Retaining ring 41 spot welded to shell 34 on the side of the dielectric spacer opposite flange 36 retains the axial relationship of the spacer on the shell. Similarly, retaining ring 42 spot welded to cylindrical section 27 of shell 21 on the side of dielectric spacer 39 opposite shoulder 26 retains the cathode support shell permanently fixed in axial relationship with shell 21. In like manner, retaining ring 43 spot welded to the outer cylindrical section 23 on the side of dielectric spacer 28 opposite shoulder 26 retains the dielectric spacer 28 in proper axial relationship on shell 21.

Within cathode support shell 34, and resting on inwardly extending flange 37, retained thereon by retaining ring 44, is dielectric support plate 46. The support plate is apertured to provide for the electrically insulated passage of heater leads 47 and 48 connecting opposite ends of heater coil 49 supported on plate 46 and extending axially away from cathode support shell 34.

Rigidly supported adjacent the end of the heater remote from the support plate 46, is cathode 51. The cathode is provided with a concave emitting surface 52 coaxially oriented with respect to aperture 33 in the focus electrode, lies closely adjacent thereto, and is supported on cylindrically extending flange 38 of cathode support shell 34. Such support of the cathode is effected by cylindn'cal shell or sleeve 53, preferably formed from Kovar, one end of which is spot Welded to the peripheral edge portion of the cathode, and the other end of which is spot welded to cylindrical flange 38. Sleeve 53 is preferably provided with reentrant portion 54 which extends downwardly toward the support shell in close proximity to the outer surface of the heater coil. Portion 54 terminates in a free end 56 spaced from the end of flange 38, and cooperates with sleeve 53 to provide a space therebetween which tends to prevent the radiation of heat transversely away from the heater coil.

In order that the spacing between focus electrode and accelerating anode, and between cathode and focus electrode, will be maintained Within permissible limits even upon heat cycling through extremes in temperature, shell 21 and shell 34 are preferably fabricated from Kovar. It has been found that by use of this material, expansion and contraction of the various parts resulting from heat cycling will increase and diminish the spacing between the cathode and focus electrode only a small amount. Where this spacing varies .009" to .075 there will be a 10 to 40 volt spread in the voltage between these elements. The construction described retains the parts against vibration in the range between 5 to 500 cycles per second at levels of acceleration up to a maximum of about 10 GS and heat cycling between 55 C. to 70 C.

To rigidly retain the electron gun assembly within the electron gun cup 2, a ceramic and metal ring complex 57 is integrally united to one end of the cup and arranged to project coaxially into the cup into tightly abutting relation with dielectric spacer 28.

The ceramic-metal ring complex comprises a plurality of axially aligned dielectric ring members 58, 59, 61, 62, 63, 64, 66, 67, 68, and 69. As shown in the drawing, one end of dielectric ring 58 abuts dielectric spacer member 28 to retain the dielectric spacer tightly abutted against shoulder 4. The other end of spacer ring 58 is integrally bonded to radially extending annular plate 71 having a cylindrically extending flange 72 on its outer periphery, one edge of which is integrally and hermetically heliarc welded to the peripheral edge of cup 2. The rigidity of this interconnection, and the thickness of the annular plate 71 insures that dielectric spacer 28 will be retained rigidly against shoulder 4.

Dielectric ring 59 is integrally and hermetically bonded to the opposite side of annular plate 71 from dielectric ring 58, and serves to electrically insulate terminal ring 73 from the body of the tube. This terminal ring is provided with a radially outwardly extending lug 74 for connection to an appropriate source of power, and with a radially inwardly extending lug 76, connected as by lead 77 with shell 21. This interconnection of terminal ring 73 with the focus electrode support shell permits energizing the focus electrode by means outside the envelope.

Dielectric rings 61 and 62 serve to integrally and hermetically isolate terminal ring 73 from terminal rings 78 and 79. Terminal ring 78 is provided with outwardly extending lug 81 and inwardly extending lug 82, the latter conductively connected by lead 83 with cathode support shell 34, which is in turn connected by lead 84 with heater lead 48.

Terminal ring 79 is provided with outwardly extending lug 86, and inwardly extending lug 87 within the ceramic metal ring complex, the latter lug being connected by conductive lead 88 with the other heater lead 47. It will thus be seen that dielectric spacer 28 and dielectric ring 58 cooperate to retain the electron gun assembly coaxially and rigidly supported within the electron gun cup 2 while electrically insulating the gun assembly from the cup. Cooperating with dielectric spacer 28 and dielectric ring 58 in this regard is dielectric ring 59 which isolates terminal ring 73 from the body of the tube and permits energizing the focus electrode with the proper voltage from outside the electron tube.

In like manner, the dielectric spacer interposed between shell 21 and shell 34, electrically insulates these shells one from the other, while retaining them in mechanically rigid and coaxial relationship. It is therefore possible to maintain the electron beam accelerating anode electrode 12 at a relatively high potential difference with respect to the cathode, without danger of shorting. In practice, the accelerating anode is preferably maintained at ground potential.

The dielectric ring 63 is integrally and hermetically interposed between terminal ring 79 and a sealed structure including radially outwardly extending annular seal plate 89 having a cylindrically extending flange 91 on its outer periphery.

In the embodiment of the gun structure shown in FIGURE 1, annular seal plate 89 snugly surrounds closure plate 92 having a cylindrical flange 93 in abutting relationship with cylindrical flange 91. To provide a hermetic and integral union between plates 89 and 92, the edges of flanges 91 and 93 are heliarc welded at 94. In the event that it subsequently becomes necessary to open the envelope, this heliarc weld may be ground or cut off and the parts disassembled. As shown in FIG- URE 1, tubulation 96 communicates with the interior of the ceramic-metal ring complex and is integrally and hermetically brazed in an appropriate aperture formed in closure plate 92. Ceramic ring 64 is interposed between seal plate 89 and closure plate 92 to retain these parts in spaced relation. This dielectric ring functions also to equalize the thermal stresses imposed on the seal between seal plate 89 and dielectric ring 63, thus helping to preserve the hermetic bond between these elements.

The embodiment of the electron gun structure shown in FIGURE 4 differs from the embodiment shown in FIGURE 1 in that the FIGURE 4 embodiment has incorporated therein a getter structure designated generally by numeral 97, and including hollow conical support shell 98, having its large base integrally supported on terminal ring 99 bonded between dielectric rings 67 and 68, and provided with outwardly extending terminal lug 101. The terminal lug 101 serves to connect the getter structure to an appropriate source of power. Within the envelope, a barium wire loop 102 is connected at one end by a lead 103 to conical support shell 98, and at its other end by lead 104 to terminal plate 106 integrally bonded to dielectric ring 68. Terminal plate 106 constitutes a closure plate corresponding to closure plate 92 in the embodiment shown in FIGURE 1, and is provided at its inner periphery with an appropriate aperture adapted to receive tubulation 96. When current of sufl'icient magnitude is caused to flow through the barium wire loop, getter material will be evaporated from the Wire and will be deposited on adjacent surfaces. In order to prevent the build-up of a conductive path between terminal rings within the ceramic-metal ring complex, a getter shield is provided constituting a conical shell 107 supported at its large base on support shell 98. As shown in the drawing, both shells are hollow and truncated, and getter shield 107 extends into the apex end of sup port shell 98 to provide therebetween an annular channel 108 having inclined surfaces 109 and 112 on which the getter material may condense. This arrangement of the parts provides a large surface are-a on which the getter material may be deposited, and serves also to shield the interior surfaces of the dielectric rings from collecting a continuous layer of the conductive getter material.

Coaxially arranged with respect to the electron gun section of the tube, is a radio frequency interaction section 116. The radio frequency interaction section includes a tubular metallic envelope portion 117, opposite ends of which are machined to provide reduced diameter portion 118 adjacent electron gun cup 2 and reduced diameter portion 119 at the opposite end. Each of the reduced diameter portions is provided with a lou gitudinally extending slot being designated 121 at the electron gun end of the envelope tube 117, and 122 at the end remote therefrom. As shown in FIGURE 1, the reduced diameter envelope portion 118 extends through the aperture in the bottom 8 of cup 2 in the form of a re-entrant portion of the cup bottom. The reduced diameter portion is extended into the cup until shoulder 123 formed between the reduced diameter portion 118 and the remainder of the envelope tube abuts the bottom. In this position the tubular envelope por tion is rigidly brazed to the bottom of the cup.

In fabricating the tubular envelope portion the length of the machined portion 118 is carefully controlled in order that the amount which the tube extends into the cup will be predetermined within close limits. Close tolerances are important in this regard because it is desirable that the inner end of the tubular envelope portion abut the accelerating anode 12. It should be noted however that while the tubular envelope portion abuts the accelerating anode 12 it is not secured thereto. It has been found that abutment of shoulder 123 against bottom 8 is also important to maintain the integral and hermetic union of the cup and tubular envelope portion at this point. The ends of the tubular envelope portion 117 remote from the electron gun is integrally united to collect-or block 124 brazed within tubular collector envelope section 126.

The collector section of the tube is preferably fabri cated as a unit with collector block 124 appropriately brazed within collector envelope section 126. The col lector block itself is provided with a longitudinally extending groove 127 milled over its entire length and extending radially thereinto to receive inner output conductor 128 in insulated relation therein. The inner conductor is preferably tubular in form and insulated from the walls of the groove by dielectric tube 129. Also formed in the collector block is a collector bore 131 having its open end 132 on the axis of the tube, the bore ranging through the block at an angle to the axis.

For facility of assembly of the collector section to the radio frequency interaction section, the collector block is provided with a portion which extends past the end of tubular envelope section 126, and proportioned to fit snugly within tubular envelope section 117. This outwardly extending portion of the collector block therefore functions to jig the parts into exact alignment. In assembling the collector assembly to the interaction sec tion, the terminal end of inner conductor 128 is oriented adjacent slot 122 formed in the end of tubular section 117. The opposite end of the inner conductor is passed through the central aperture in dielectric plug 132 which has its outer peripheral edge integrally and hermetically brazed to the interior of collector envelope section 126 adjacent the outer end thereof. A pin seal 133 is brazed to the outer end of the inner conductor and to a surface portion 134 of the dielectric plug surrounding the inner conductor. This arrangement of the parts integrally and hermetically seals this end of the envelope structure. An output connector 136 is brazed to pin 133 to provide a detachable connection with the inner con ductor of an associated transmission line.

Mounted within tubular envelope section 117, is a slow wave structure comprising helical conductor 137 ccaxially supported within the tubular envelope section by dielectric rods 138 and resilient spring clips 139. A pyrolytic carbon coating 140 on the rods extending over a greater portion of their length functions to attenuate the wave in a well known manner. The cooperative relationship of these elements is best shown in FIGURES l and 3.

The end of the helix remote from the electron gun is provided with a radially extending section 141 terminating in a longitudinally extending section 142 which extends into the end of tubular inner conductor 128. This interconnection is appropriately made through the access aperture formed by slot 122 in the outer end of tubular envelope section 117. After the terminal end of the helix is inserted into the tubular inner conductor, the union between these two elements is made integral and continuous by suitable spot welding. After such spot welding, a cylindrical sleeve 143, which during assembly has rested on the reduced diameter portion of collector section 126, is slid forward into abutting relation with the shoulder formed on tubular section 117 to overlie or cover slot 122. The sleeve is brazed in this position to hermetically close the access aperture 122.

At its input end the helical conductor extends through bottom wall 8 of electron gun cup 2. The radially extending terminal end of the helical conductor extends into one end of tubular input conductor 146 extending through dielectric plug 147 carried within cylindrical metallic sleeve 148 integrally and hermetically brazed within an appropriate aperture formed in the side wall of cup 2. The sleeve 148 is itself brazed within outwardly extending support collar or post 149 brazed at one end to the side wall of the cup 2. Within the envelope, dielectric plug 147 is appropriately tapered as shown in FIGURE 1 to provide a transition match between the input transmission line and the slow wave structure. This matching of the impedance of the input line with the helical conductor is aided by means of metallic strap 150 brazed at one end to sleeve 143 and conforming for a portion of its length to the taper of the inner end of dielectric plug 147, the other end of the strap being integrally brazed to the accelerating anode support shell 16.

Outside the envelope, an input terminal designated generally by the numeral 152, is provided with a central pin connector 153 integrally brazed to the end of inner conductor 146. The end of the pin connector is also brazed to the surface of dielectric plug 147 to hermetically seal the union between inner conductor and plug, The input pin connector 153 is reinforced by a dielectric bushing 154 and is provided with resilient contact fingers 156 for resilient detachable connection to the inner conductor of an associated transmission line. The outer conductor of the input terminal is formed by a sleeve 157 brazed at one end to electron gun cup 2 about collar 149 and provided adjacent its other end with threads 158 for detachable connection to the corresponding outer conductor of an associated transmission line.

It should be noted that as each of the sub-assemblies of the electron tube is fabricated, each is capable of being individually leak-checked to determine its ability to maintain a vacuum. After the sub-assemblies are assembled and hermetically united to form the completed envelope, the envelope is evacuated through tubulation Q6. It has been found that assembly of tubes in this manner assures that the envelope of each tube will be vacuum tight upon final seal.

At this stage in the assembly, the beam tube appears as shown in FIGURE 2. It is now ready for application of the magnetic circuitry thereto. Supported on the exterior surface of the radio frequency interaction section is a permanent periodic magnet stack comprising a plurality of permanent ferrite magnets 161 in the form of thin annular wafers separated by magnetizable pole pieces 162, also in the form of annular members. The inner periphery of each of pole pieces 162 is provided with a cylindrical flange portion 163 extending on both sides of pole piece 162 and cooperating with adjacent pole pieces to provide gaps 164 therebetween. The outer peripheries of the annular pole pieces are interconnected by a plurality of circumferentially arranged ferromagnetic compensating strips 166 extending over the length of the stack.

The permanent magnet wafers 161 are preferably arranged one with the other to orient like poles of adjacent magnets in abutting relation. The compensating strips 166 are preferably formed from a nickel-iron alloy chosen to provide compensation for the reduced magnetic field force at elevated temperatures, It has been found that at elevated temperatures the force of the fields between the inner peripheries of the pole pieces tends to diminish. This diminishing elfect is lessened by the compensating strips connecting the outer peripheries of pole pieces increasing the resistance to magnetic flux at elevated temperatures. In this manner the force of the magnetic fields tending to confine the electron beam remains substantially constant through temperature cycling of the tube.

To maintain the magnetic stack immobile on the smooth cylindrical surface of the-interaction section of the tube, a seal plate 167, formed preferably from a dielectric material such as Teflon, is pushed over the end of the collector envelope section into close abutting relationship with the magnetic stack. The seal plate is annular in form as shown, and the inner periphery forms a snug sliding fit with the outer periphery of collector portion 126. Over the seal plate is slipped a cylindrical encapsulating sleeve 1'68 fixed at one end to cooler structure 169 by screws 170. The other end of sleeve 168 surrounds the electron gun cup in radially spaced relation thereto. Integrally united with this end of encapsulating sleeve 168, in overlapping relation therewith, is an encapsulating sleeve extension 171. The sleeve 171 is also radially spaced about the electron gun cup 2 and during fabrication is temporarily held in position by an appropriate jig which retains the electron gun cup coaxially centered within the encapsulating sleeves. The sleeve 171 terminates just short of the open end of the gun cup 2, and is provided adjacent its outer end with an internal groove 172. With the encapsulating sleeve and tube held in this relationship, a suitable potting mixture or encapsulating synthetic resin in liquid form is pumped through an aperture 173 in sleeve 168 adjacent seal plate 167. The encapsulating synthetic resin fills the annular space between both of the encapsulating sleeves and the associated tube structure, filling all of the crevices and forcing the air from this space. This operation is preferably performed while the tube with its encapsulating sleeve attached is held in an upright position with the collector extending downwardly. In this manner, when the encapsulating synthetic resin reaches the jig holding the electron tube centrally positioned within the encapsulating sleeve 169, the space in and around the magnetic stack and electron gun cup 2 will be completely filled with encapsulating fluid. This encapsulating fluid is preferably a type which rapidly solidifies to provide an impenetrable mass 174. The encapsulating material holds the magnetic stack immobile and at the same time tends to absorb impact shocks which might inadvertently be delivered to the encapsulating sleeves.

The cooler is preferably adapted to be detachably secured to the collector section 126, and is provided with radially extending fins 176 through which cooling air may be circulated. In addition to connection of the cooler structure to encapsulating sleeve 168 by screws 170, the cooler structure is provided with tangentially extending clamp screws (not shown) to tightly bind the cooler structure on the smooth cylindrical envelope portion in heat transfer relation. Detachably mounted on the cooler structure and in conductive electrical contact with the terminal end of the collector envelope section 126 is a coaxial output coupling provided with the radially extending flange 177 and a cylindrical threaded portion 17 8 for connection to a conventional connector fitting on an associated trasmission line.

The assembly of the tube is completed by connection of appropriate leads 179 to the terminal lugs 74, 81 and 86. The gun end of the tube is then appropriately surrounded with a mold, not shown, and the mold is filled with an encapsulating rubber material 181. In this way the terminal lugs are electrically insulated from the body portion of the electron gun and encapsulating sleeve, and are also held against mechanical vibration and impact shock. Additionally, since the encapsulating rubber surrounds the tubulation which, as is well known in the art, is susceptible of being ruptured, the tubulation is also protected and the entire gun end of the tube is less susceptible to being damaged by impact shocks. The tube so formed with its associated circuitry thereon may be mounted in a suitable manner on supporting structure.

We claim:

1. Wave transmission apparatus comprising an evacuated envelope enclosing an electron gun for projecting an electron beam and a collector for collecting the beam, interaction means operatively interposed between the gun and collector arranged to provide interaction between the electron beam and an electromagnetic wave transmitted therealong, said interaction means having a tubular envelope shape, electromagnetic wave input and output coupling means operatively associated with opposite ends of the interaction means, a plurality of magnetic rings and pole pieces stacked on said tubular envelope between said gun and said collector, a body of solid dielectric material surrounding said magnetic rings and pole pieces and a portion of said gun, and sleeve means around said dielectric material for enabling the dielectric material to be applied in liquid form and to form a rigid outer support for interconnecting said gun and said interaction means.

2. A traveling wave tube comprising an evacuated envelope including an electron gun section and collector section spaced apart and hermetically united to opposite end portions of an intermediate tubular envelope section, said electron gun section including a hollow cup having a centrally apertured solid bottom through which an end of the intermediate tubular envelope section extends, said hollow cup characterized as having at least one shoulder portion on the interior thereof, an electron gun assembly within the electron gun section and including an accelerating anode shiftably abutting the associated end of the intermediate tubular envelope section, dielectric spacing means interposed between said cup and said electron gun assembly and abutting said shoulder for rigidly retaining the electron gun assembly coaxially within said electron gun section, a slow wave structure within the envelope, and electromagnetic wave input and output coupling means on the envelope operatively associated with opposite ends of the slow wave structure.

3. A traveling wave tube comprising an evacuated envelope including an electron gun section and collector section spaced apart and hermetically united to opposite end portions of an intermediate tubular envelope section, said electron gun section including a hollow cup having an apertured bottom hermetically associated with an end portion of the intermediate tubular envelope section, said hollow cup characterized as having at least one shoulder portion on the interior thereof, an electron gun assembly within the electron gun section and including an accelerating anode spaced from said cup, annular dielectric spacer means interposed between said cup and said electron gun assembly and abutting said shoulder for rigidly retaining said electron gun assembly coaxially within said electron gun section, a slow wave structure within the envelope having one end terminating in the space between the accelerating anode and said cup, and electromagnetic wave input and output coupling means on the envelope operatively associated with opposite ends of the slow wave structure, said input coupling including a substantially constant impedance transition portion extending radially through the envelope in the space between the anode and bottom of the cup, annular magnetic means around said tubular envelope section, dielectric encapsulating material around said magnetic means and a portion of said cup, and a cylinder around said dielectric encapsulating mate rial in contact therewith.

4. An electron gun comprising a supporting housing, an electron beam forming electrode assembly including a first hollow shell symmetrical about a longitudinal axis, a first support plate supportingly interposed between the first shell and the housing, a focus electrode supported adjacent one end of the first shell, an anode spaced from said focus electrode, a second support plate supportingly interposed between said anode electrode and said housing, a third support plate mounted inside and adjacent the opposite end of the first shell, a second hollow shell mounted on the third support plate, a cathode supported on one end of the second shell in operative proximity to the focus electrode, energizable heater means operatively associated with the cathode and supported on the housing, a plurality of alternate ceramic and metal rings stacked coaxially together in hermetically sealed relation, selected ones of said metal rings constituting external terminals for selected ones of said electron gun electrodes being electrically interconnected therewith, and an end plate structure hermetically sealing the end of the ceramic-metal ring stack remote from the housing, said housing having a first shoulder on its inner periphery, said first support plate being in abutment with said first shoulder, said housing having a second shoulder on its inner periphery of smaller diameter than the first shoulder, and said second support plate being in abutment with said second shoulder.

5. A traveling wave tube comprising an evacuated envelope including an electron gun section and collector section spaced apart and hermetically united to opposite end portions of an intermediate tubular section, said evacuated envelope initially having an access aperture adjacent said collector section, an electron gun assembly within the envelope, a helix slow wave structure within the envelope and having one end thereof terminating adjacent said access aperture, a coaxial output having a center conductor, said center conductor and said one end of the helix being joined together adjacent said initially open access aperture in the envelope, an input coupling connected to the other end of said helix, and a sleeve around the envelope hermetically sealing said access aperture before evacuation of the envelope and after union of said one end of the helix and said output center conductor, said sleeve being slidable along the envelope prior to being sealed in position.

References Cited by the Examiner UNITED STATES PATENTS 2,886,742 5/1957 Hull 315 37 2,932,767 4/1960 Van Goor et a1. 315- 39 2,955,224 10/1960 Marchese 33334X 2,964,670 12/1960 Bliss 315 3.5 2,970,240 1/1961 Iversen 315-35 2,984,762 5/1961 Haas 315 3.5 2,992,348 7/1961 Okstein 315-35 x 3,002,122 9/1961 Unger 313 312 3,020,440 2/1962 Chang 315 -3.5

ELI LIEBERMAN, Acting Primary Examiner.

GEORGE N. WESTBY, Examiner. 

1. WAVE TRANSMISSION APPARATUS COMPRISING AN EVACUATED ENVELOPE ENCLOSING AN ELECTRON GUN FOR PROJECTING AN ELECTRON BEAM AND A COLLECTOR FOR COLLECTING THE BEAM, INTERACTION MEANS OPERATIVELY INTERPOSED BETWEEN THE GUN AND COLLECTOR ARRANGED TO PROVIDE INTERACTION BETWEEN THE ELECTRON BEAM AND AN ELECTROMAGNETIC WAVE TRANSMITTED THEREALONG, SAID INTERACTION MEANS HAVING A TUBULAR ENVELOPE SHAPE, ELECTROMAGNETIC WAVE INPUT AND OUTPUT COUPLING MEANS OPERATIVELY ASSOCIATED WITH OPPOSITE ENDS OF THE INTERACTION MEANS, A PLURALITY OF MAGNETIC RINGS AND POLE PIECES STACKED ON SAID TUBULAR ENVELOPE BETWEEN AND GUN AND SAID COLLECTOR, BODY OF SOLID DIELECTRIC MATERIAL SURROUNDING SAID MAGNETIC RINGS AND POLE PIECES AND A PORTION OF SAID GUN, AND SLEEVE MEANS AROUND SAID DIELECTRIC MATERIAL FOR ENABLING THE DIELECTRIC MATERIAL TO BE APPLIED IN LIQUID FORM AND TO FORM A RIGID OUTER SUPPORT FOR INTERCONNECTING SAID GUN AND SAID INTERACTION MEANS. 